1. Field of the Invention
The present invention relates to wire clamps for wire bonders and more particularly to an improved wire clamp assembly which is provided with a self-aligning feature for use on existing or new automatic wire bonders.
2. Description of the Prior Art
The present invention is an improvement of the "voice coil actuated fine wire clamp" shown and described in our U.S. Pat. No. 4,653,681 which is assigned to Kulicke & Soffa Industries, Inc., the same assignee as the present invention. Such prior art wire clamps are placed on automatic wire bonders that are capable of producing eight wire bonds every second in a preferred bonding mode. The wire clamps open and close once for every wire bond. It is not unusual for such wire bonders to be operated over 70 to 75% of the time when used continuously over more than one full production shift. This implies that one-quarter billion movements of the actuating levers of the wire clamps take place over one year on one shift alone. The jaws of the prior art wire clamps were designed to close and clamp a wire while having the clamping faces of the jaws actuated in substantial parallel alignment. The moving part of the wire clamps were pivoted on pivot bearings which may be lubricated, however, the jaw of the wire clamps are not lubricated and are subject to wear and require replacement.
Worn prior art wire clamps must be replaced before they cease to function properly and cause damage to valuable semiconductor product. It is extremely difficult to inspect the prior art wire clamp jaws to determine whether they are becoming inoperable. Once the jaws of the prior art wire clamps become inoperable, production is interrupted and if the wire bonder is part of an integrated production line of equipment, the whole line is usually interrupted or at least delayed.
There are basically two types of wire clamps from the service and maintenance point of view. Wire clamps that are provided with replaceable jaw elements are mounted on supporting structural elements. When the jaws of such wire clamps become inoperable, the wire bonder is stopped and the worn jaws are removed. The new jaws are attached to the wire clamp system and then the maintenance engineer must physically measure the clearance between the jaw elements and also attempt to physically bend and align the jaw support elements. This latter task is sheer guess work for there is no known way to visually measure parallelism between jaws of wire clamps without special calibration tools. Usually the replaceable jaws replacement period is predicated on a preventive maintenance schedule.
Wire clamps are assumed to be parts which wear out and are replaced after a predetermined number of hours. The wire clamp assembly shown in U.S. Pat. No. 4,653,681 are mounted on a bond head link or bracket and are detachable from the wire bonder and replaced as a unit. When the jaws are made of very hard material such as synthetic jewels, the maintenance-replacement period is so long that it can be scheduled to occur during a scheduled down time and the wire bonder does not cause rejected product or interruption of the integrated production line. While this latter type of service maintenance is not only more cost efficient, it avoids the possible destruction of valuable integrated circuit devices that were otherwise perfectly acceptable if not abused in an automatic wire bonder which is not in proper adjustment.
It would be desirable to provide a wire clamp assembly that embodies all the desirable and reliable features of the detachable wire clamp system as the type shown in U.S. Pat. No. 4,653,681 and would also permit rapid and accurate replacement of the jaws without replacement of the wire clamp system and without the need for a highly skilled technician or even the need for precision instruments to make critical adjustments.